The invention relates to a knife holder for a circular wrapper cutter, positioned so as to rotate inside a knife head, for the lengthwise separation of material webs, in particular material webs made of paper or plastic foil, wherein the circular wrapper cutter is provided with a hand guard.
Narrow material strips are produced from the originally wide material webs by separating material webs in lengthwise direction with the aid of circular wrapper cutters that operate according to the scissor cut method, wherein the strip width depends on the respective application case. In order to produce the narrowest possible strips or ribbons, the knife holders that must be arranged side-by-side on a knife holder bar, at a corresponding distance to each other, should have the narrowest possible overall width since the minimum possible cutting width is essentially determined by this overall width. For reasons of operational safety, it is particularly important that the worker be protected during the adjustment operations against injuries caused by the circular wrapper cutter, wherein it is known to provide the circular wrapper cutter with a cover that is adjustable if necessary. Depending on the cover design, the problem arises that the overall width of the knife holder is increased, thereby causing a decrease in the minimum possible cutting width.
The German Patent DE-PS 37 12 078 discloses a knife holder for reel cutters with a hand guard, complemented by at least one box-type segment on the side facing the counter cutter. This box-type segment can be operated via a separate piston-cylinder unit that is connected in series with the piston-cylinder unit. In the circular cutter position where the circular cutter is lifted off the counter cutter, the box-type segment is closed via spring force. During the movement for lowering the circular cutter, both piston cylinder units are admitted with hydraulic fluid, so that the box-type segment pivots into the hand guard and exposes the blade of the circular cutter. In addition to the high design expenditure for an additional piston cylinder unit, such a knife holder has the disadvantage of requiring a larger overall width for the knife holder.
A similar arrangement with a two-part protective hood is disclosed in the European Patent EP-A-0 562 454, wherein the part of the protective hood which faces the counter cutter and is designed as box-type segment provided with a slot is positioned such that it can be displaced vertically. The box-type segment in this case is also moved with the aid of a separate piston-cylinder unit. In the position where the circular cutter is raised, the box-type segment is held in the closed position with the aid of a closing spring and is pulled back with the aid of the piston during the lowering movement, so that the blade of the circular cutter can extend through the slots. A hand guard designed in this way is expensive and subject to malfunctions because of the multi-part design and the necessary complicated adjustment mechanism.
The EP-A-0 333 001 discloses a knife holder with a protective hood as hand guard. This hood is attached stationary to the base body of the knife holder and covers the circular cutter completely when it is in the raised position. When the circular cutter is lowered toward the counter cutter, the circular cutter moves out of the stationary protective hood.
The reference DE-U-90 12 926 also discloses a knife holder for reel cutters where the circular cutter is surrounded on the side as well as on the side facing away from the counter cutter by a fixed hand guard and where the cutting range of the knife is covered by a movable segment which is also opened and closed with the aid of an involved operating device.